Piezoelectric component and manufacturing method thereof

ABSTRACT

A piezoelectric component having resonance characteristics adjusted to a high degree of accuracy is provided. A piezoelectric substrate is provided with a resonating part. A deposit is added onto a surface of the resonating part and is provided with a plurality of indented portions at its surface enclosed by outer edges. The deposit is constituted of a resin which may contain a carbon filler. The indented portions are formed through laser machining.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric component and a methodfor manufacturing the piezoelectric component.

2. Discussion of Background

Piezoelectric components have been widely employed in various types ofelectronic devices such as filters, resonators or oscillators in theprior art. A basic requirement that must be fulfilled by a piezoelectriccomponent is that, since desired characteristics are achieved byutilizing the resonance characteristics, the degree of accuracy of itsresonance frequency be high.

The following three methods are well known as means for achievingdesired resonance characteristics by adjusting the resonance frequencyof a piezoelectric component. In the first method, the thickness of thepiezoelectric substrate is adjusted through polishing. In the secondmethod, the thickness of the electrode is adjusted and in the thirdmethod, the desired resonance characteristics are achieved through theadjustment of the quantity of resin deposited onto the resonating part.

However, the first method poses problems in that it is difficult toperform polishing at the accuracy required for adjusting the resonancefrequency and in that inconsistency occurs in the resonance frequency.The second method requires a great length of time and a great deal ofwork and, furthermore, it does not achieve good reproducibility. Thethird method presents a problem in that it is difficult to finely adjustthe quantity of resin to be deposited onto the resonating part.

An improvement on the third method is disclosed in, for instance,Japanese Unexamined Patent Publication No. 160121/1981. This publicationdiscloses a method whereby the resonance frequency of a piezoelectricsubstrate to which a mass substance is added in advance is measured, acorrect quantity of the mass substance is removed by radiating a laserbeam which is controlled in correspondence to the degree of deviation ofthe resonance frequency relative to the frequency setting on the masssubstance added to the piezoelectric substrate to adjust the resonancefrequency to the frequency setting.

However, the publication does not refer to specifically how the masssubstance should be processed or what type of laser beam should beemployed. Consequently, the method disclosed in the publication above isnot sufficient to provide a piezoelectric component with a high degreeof accuracy in the resonance frequency and a high Q value for itsresonance characteristics.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a piezoelectriccomponent having a resonance frequency which is adjusted with a highdegree of accuracy.

It is a further object of the present invention to provide apiezoelectric component with a high degree of accuracy in its resonancefrequency and a high Q value for its resonance characteristics.

It is a still further object of the present invention to provide amethod for manufacturing piezoelectric components in large quantitiesthat are free of inconsistency in their characteristics through simpleprocesses.

In order to achieve the objects described above, the piezoelectriccomponent according to the present invention includes a piezoelectricsubstrate and a deposit. The piezoelectric substrate is provided with atleast one resonating part. The deposit is added onto a surface of theresonating part and is provided with a plurality of indented portionswithin a surface enclosed by outer edges.

Since the deposit is added onto the surface of the resonating part, asdescribed above, a load corresponding to the mass of the deposit isapplied to the resonating part to set the resonance frequency of theresonating part at a value that corresponds to the mass of the depositand the load.

Since the deposit is provided with a plurality of indented portionswithin its surface enclosed by the outer edges, the resonance frequencyis set at a value with a high degree of accuracy that corresponds to thenumber of indented portions, the volume of the indented portions, thedistance between the individual indented portions, the pattern of theindented portions and the like.

The indented portions are formed so that the load applied by the depositto the resonating part is evenly distributed at the surface of theresonating part. Evenly distributing the load in this manner contributesto achieving a higher accuracy in the resonance frequency.

In the method for manufacturing a piezoelectric component according tothe present invention, during the step for adjusting the resonancefrequency of the piezoelectric component, a laser beam whose wavelengthis within a range of 350 to 2000 nm is radiated onto a surface of thedeposit and the deposit is trimmed through being irradiated by the laserbeam to form indented portions. Thus, the mass of the deposit is reducedin correspondence to the number of indented portions, the size of theindented portions, the distance between the individual indentedportions, the pattern of the indented portions and the like to adjustthe load applied by the deposit to the resonating part.

Since the indented portions are formed through radiation of a laserbeam, their quantity, size, pattern and the like can be set with a highdegree of accuracy. As a result, the resonance frequency can be set at avalue with a high degree of accuracy.

For the formation of the indented portions, a laser beam having awavelength within the range of 350 to 2000 nm is radiated. By using alaser beam having a wavelength within this range, indented portions canbe formed at the deposit without resulting in any degradation in thepiezoelectric characteristics.

It is desirable that the deposit be constituted of resin. Byconstituting the deposit of resin, the required indented portions can beformed with ease through radiation of a laser beam. It is particularlydesirable to use a resin containing a carbon filler at 0.1 to 20 wt %.Since the degree to which a laser beam is absorbed by resin can beadjusted in correspondence to the carbon filler content, the intensityof the required laser beam can be indirectly adjusted by using a resincontaining a carbon filler at 0.1 to 20 wt %.

A suitable laser to be employed is a solid-state YAG laser. Inparticular, the fundamental harmonic (wavelength; 1.06 μm), the secondharmonic (wavelength; 530 nm) or the third harmonic (wavelength; 353 nm)of a solid-state YAG laser is ideal.

Furthermore, the present invention discloses a technology for adjustingthe resonance frequency without lowering the Q value of a piezoelectriccomponent with an even higher degree of accuracy. This technology may beadopted in an ideal manner when adjusting the resonance characteristicsof an oscillator, a resonator or the like that requires highly accurateadjustment of the resonance characteristics.

In the piezoelectric component according to the present invention, thesurface of the deposit is scored with indentations and projections, andwhen the surface roughness of the indented and projected surface isassigned Rmax and the resonance wavelength of the resonating part isassigned λ₀, a relationship expressed as Rmax/λ₀ ≦0.008 is satisfied.

With the surface of the deposit constituted of indentations andprojections, the mass of the deposit can be finely controlled incorrespondence to the state of the indentations and projections at thesurface of the deposit to achieve fine and highly accurate adjustment ofthe resonance frequency.

The Q value of the resonance characteristics is greatly affected by thestate of the indentations and projections at the surface of the deposit.When standardized surface roughness R₀ is defined as (Rmax/λ₀) with Rmaxbeing the surface roughness of the indented and projected surface and λ₀being the resonance wavelength of the piezoelectric component, in therange over which the standardized surface roughness R₀ is at 0.008 orless, an almost constant high Q value can be achieved regardless of anyfluctuation in the standardized surface roughness R₀. In the range overwhich the standardized surface roughness R₀ is at 0.008 or more, the Qvalue is reduced almost exponentially as the standardized surfaceroughness R₀ increases.

In order to obtain a piezoelectric component with the surface of itsdeposit constituted of indentations and projections, a laser beam havinga wavelength of 350 nm or less is irradiated on the deposit to trim thesurface of the deposit.

With a laser beam having a wavelength of 350 nm or less, the surface ofthe deposit can be trimmed evenly to achieve a standardized surfaceroughness R₀ of 0.005 or less, which makes it possible to achieve highaccuracy in the resonance frequency and a high Q value. It has beenconfirmed that when trimming is performed using a laser beam having awavelength longer than 350 nm, e.g., a laser beam having a wavelength of353 nm, the Q value becomes lower.

It is desirable to measure the resonance frequency of the piezoelectriccomponent and radiate a laser beam controlled in correspondence to thedegree of deviation of the measured resonance frequency relative to thetarget resonance frequency on the deposit during the trimming process.Through this adjustment method, the resonance frequency can be adjustedto the target resonance frequency with ease.

By repeating the adjustment described above, the accuracy of theresonance frequency adjustment can be improved. During this process, ifthe wavelength of the laser beam radiated on the deposit is 350 nm orless, only an extremely small quantity of the laser beam is converted toheat. Thus, even immediately after radiation of the laser beam, theresonance frequency of the piezoelectric component can be measured.Consequently, the trimming adjustment process employing the laser beamcan be repeated without allowing intervals.

The laser beam employed for the trimming may be set in either thesingle-mode or the multi-mode. Since the intensity of the laser beam isdistributed evenly within the spot when set in multi-mode, trimming canbe performed more consistently through radiation of laser beam in themulti-mode to achieve a piezoelectric component with a high degree ofaccuracy in its resonance frequency and a high Q value for its resonancecharacteristics.

Alternatively, trimming may be achieved by scanning the laser beam spotover the entire surface of the deposit evenly. In this case, thequantity of shift in the resonance frequency per scan is constant. As aresult, by selecting the number of scans to be performed with the laserbeam spot, the resonance frequency can be adjusted.

In addition, to irradiate the deposit, a pulse oscillation type lasersystem may be employed to radiate a pulse laser beam over the entiresurface of the deposit evenly.

As described above, the quantity of shift in the resonance frequency perlaser beam irradiation is constant. Consequently, the resonancefrequency can be adjusted in correspondence to the number of times thatthe pulse laser beam is radiated.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages, features and objects of the presentinvention will be understood by those of ordinary skill in the artreferring to the annexed drawings, given purely by way of non-limitativeexample, in which;

FIG. 1 is a plan view of the piezoelectric component according to thepresent invention;

FIG. 2 is an enlarged sectional view of the piezoelectric componenttaken along line 2--2 in FIG. 1;

FIG. 3 is a plan view of the piezoelectric component in FIGS. 1 and 2,in a state before the deposits are added;

FIG. 4 is a bottom view of the piezoelectric component illustrated inFIG. 3;

FIG. 5 is an electrical symbol diagram of the piezoelectric component inFIGS. 3 and 4;

FIG. 6 is a plan view illustrating another embodiment of thepiezoelectric component according to the present invention;

FIG. 7 is a plan view of a piezoelectric component for which centerfrequency adjustment is performed;

FIG. 8 illustrates a method for center frequency adjustment performed onthe piezoelectric component shown in FIG. 7;

FIG. 9 illustrates the relationship between the number of grooves andthe quantity of center frequency shift (kHz);

FIG. 10 is a graph illustrating the distribution of center frequencies;

FIG. 11 is a plan view illustrating another embodiment of thepiezoelectric component according to the present invention;

FIG. 12 is a bottom view of the piezoelectric component in FIG. 11;

FIG. 13 is a sectional view of the piezoelectric component taken alongline 13--13 in FIG. 11;

FIG. 14 is a schematic sectional view illustrating the indentations andprojections at the surface of the deposit;

FIG. 15 illustrates the relationship between the standardized surfaceroughness R₀ and the Q value;

FIG. 16 illustrates a piezoelectric component for which the resonancefrequency adjustment is performed;

FIG. 17 illustrates a method of the resonance frequency adjustmentperformed on the piezoelectric component illustrated in FIG. 16;

FIG. 18 presents data illustrating the relationship between the lengthof elapsed time (sec) and the resonance frequency shift quantity (%);

FIG. 19 illustrates the laser intensity characteristics in the directionof the radius of the spot of a single-mode laser beam;

FIG. 20 illustrates the laser intensity characteristics in the directionof the radius of the spot of a multi-mode laser beam;

FIG. 21 schematically illustrates the state achieved when the deposit 2is trimmed by using a single-mode laser beam at the fundamental harmonic(wavelength; 1.06 μm) of a solid-state YAG laser;

FIG. 22 schematically illustrates the state achieved when the deposit 2is trimmed by using a single-mode laser beam at the fourth harmonic(wavelength; 266 nm) of a solid-state YAG laser;

FIG. 23 schematically illustrates the state achieved when the deposit 2is trimmed by using a multi-mode laser beam at the fourth harmonic(wavelength; 266 nm) of a solid-state YAG laser;

FIG. 24 illustrates the relationship between the number of full-surfacescans and the quantity of resin trimmed in the direction of the depth ofthe resin constituting the deposit;

FIG. 25 illustrates the relationship between the number of full-surfacescans and the quantity of shift in the resonance frequency (kHz);

FIG. 26 presents data illustrating the relationship between thestandardized surface roughness R₀ and the Q value; and

FIG. 27 presents a graph illustrating the distribution of the resonancefrequencies.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 illustrate an example of a ceramic filter. It is to benoted, however, that the component may be an oscillator, a resonator orthe like instead. The piezoelectric component in the figures includes apiezoelectric substrate 1 constituted of ceramic and deposits 21 and 22.The piezoelectric substrate 1 is provided with two resonating parts 11and 12. The deposit 21, which is added onto a surface of the resonatingpart 11, is provided with a plurality of indented portions 210 in itssurface enclosed by outer edges. The indented portions 210 are formed asgrooves. The deposit 21 is divided into a plurality of divided portions211 to 216 by the groove-like indented portions 210.

The deposit 22, which is added onto a surface of the resonating part 12,is also provided with a plurality of indented portions 220 in itssurface enclosed by outer edges. The indented portions 220 are formed asgrooves. The deposit 22 is divided into a plurality of divided portions221 to 226 by the groove-like indented portions 220.

The height of the divided portions 211 to 216 and 221 to 226 should beset at approximately 10 to 20 μm. The width of the groove-like indentedportions 210 and 220 may be set at, for instance, approximately 30 μm.The shapes of the indented portions 210 and 220 and the divided portions211 to 216 and 221 to 226 are not limited to the linear shapeillustrated in the figures, and they may take any arbitrary patternincluding curves, diagonal lines, broken lines and the like. Theindented portions 210 and 220 may be constituted of holes passingthrough the deposits 21 and 22 respectively or they may be constitutedof non-through holes whose depth is smaller than the thickness of thedeposits 21 and 22.

As described above, since the deposits 21 and 22 are added onto thesurfaces of the resonating parts 11 and 12 respectively, loads thatcorrespond to the masses of the deposits 21 and 22 are applied to theresonating parts 11 and 12 to set the resonance frequencies of theresonating parts 11 and 12 to values corresponding to the masses of thedeposits 21 and 22.

Since the deposit 21 on the resonating part 11 is provided with aplurality of indented portions 210 in its surface enclosed by the outeredges, the resonance frequency is set to a high accuracy valuecorresponding to the number of indented portions 210, the size of theindented portions 210, the distance between the individual indentedportions, the pattern of the indented portions 210 and the like. In theembodiment, since the deposit 21 is divided into a plurality of dividedportions 211 to 216 by the plurality of indented portions 210, theresonance frequency of the resonating part 11 is set to a high accuracyvalue that corresponds to the number of the divided portions 211 to 216,the number of the indented portions 210 between the individual dividedportions 211 to 216, the masses of the individual divided portions 211to 216, the pattern of the divided portions 211 to 216 and the like.

Since the deposit 22 on the resonating part 12, too, is divided into aplurality of divided portions 221 to 226, the resonance frequency of theresonating part 12, too, can be set to a high accuracy valuecorresponding to the number of the divided portions 221 to 226, thenumber of indented portions 220, the masses of the individual dividedportions 221 to 226, the pattern of the divided portions 221 to 226 andthe like.

The deposits 21 and 22 are formed so that the patterns achieved by thedivided portions 211 to 216 and 221 to 226 divided by the indentedportions 210 and 220 respectively form stripes, for instance. Byachieving such stripe patterns, loads applied to the resonating parts 11and 12 by the divided portions 211 to 216 and 221 to 226 can be evenlydistributed at the surfaces of the resonating parts 11 and 12.Distributing the loads evenly contributes to achieving a higher degreeof accuracy in the resonance frequencies. However, patterns includinglattice patterns, island-like patterns and the like, other than stripepatterns, may be adopted.

FIG. 3 is a plan view of the piezoelectric component shown in FIGS. 1and 2 before the deposits are added and FIG. 4 is a bottom view of thepiezoelectric component illustrated in FIG. 3. The piezoelectricsubstrate 1 is formed in a plate shape using a piezoelectric ceramicmaterial known in the prior art. The resonating part 11 includes splitelectrodes 111 and 112 and a common electrode 113. The split electrode111 and the split electrode 112 are formed at a front surface of thepiezoelectric substrate 1 with a gap G1 formed between them. The commonelectrode 113 is provided at the rear surface of the piezoelectricsubstrate 1 at a position facing opposite the split electrodes 111 and112.

The resonating part 12 includes split electrodes 121 and 122 and acommon electrode 123. The split electrode 121 and the split electrode122 are formed at the front surface of the piezoelectric substrate 1with a gap G2 formed between them. The common electrode 113 is providedat the rear surface of the piezoelectric substrate 1 at a positionfacing opposite the split electrodes 121 and 122.

The split electrode 111 belonging to the resonating part 11 is connectedto an input/output terminal electrode 13, whereas the split electrode112 is connected to the split electrode 122 at the resonating part 12via a lead electrode 141, a capacitor electrode 15 and a lead electrode142. The split electrode 121 at the resonating part 12 is connected toan input/output terminal electrode 16 via a lead electrode 143.

The common electrodes 113 and 123 provided at the rear surface of thepiezoelectric substrate 1 are connected to a terminal electrode 17through lead electrodes 144 and 145 respectively. In addition, acapacitor electrode 18 is provided at the rear surface of thepiezoelectric substrate 1. This capacitor electrode 18 faces oppositethe capacitor electrode 15 provided at the front surface, and isconnected to the terminal electrode 17 through a lead electrode 146. Theterminal electrode 17 is made to be continuous with a common terminalelectrode 19 provided at the front surface by a through hole conductor(not shown) that passes through the piezoelectric substrate 1 in itsthicknesswise direction or the like.

Although not shown, the deposits 21 and 22 may be added onto the commonelectrodes 113 and 123 respectively provided at the rear surface as wellas onto the split electrodes (111, 112) and (121, 122) provided at thefront surface, or the deposits 21 and 22 may be added onto the commonelectrodes 113 and 123 only.

The deposits 21 and 22, which are constituted of resin, are adhered ontothe resonating parts 11 and 12 by employing a means such as coating. Byconstituting them of resin, a correct load for resonance frequencyadjustment can be achieved and, at the same time, a sufficient degree ofadhesion to the piezoelectric substrate 1 is achieved. The resin maycontain a carbon filler. A desirable carbon filler content is within therange of 0.1 to 20 wt %. By selecting the content of the carbon fillerwhose specific gravity is different from that of the resin within therange described above, the masses of the deposits 21 and 22 are adjustedso that the resonance frequencies at the resonating parts 11 and 12 canbe finely adjusted accordingly.

Furthermore, when the carbon filler content is within the range of 0.1to 20 wt %, frequency adjustment through trimming can be implemented ina stable manner. Moreover, it is possible to maintain the specificresistivity of the deposits 21 and 22 at a high value, exceeding 10¹⁴(ohm·cm) to prevent the deposits 21 and 22 from electrically affectingthe electrodes constituting the resonating parts 11 and 12. In the rangeover which the carbon filler content is less than 0.1 wt % and in therange over which the carbon filler content exceeds 20 wt %, theabsorption of the laser beam is unstable and the quantity of thefrequency shift relative to the unit trimming quantity fluctuates.Furthermore, when the carbon filler content exceeds 20 wt %, therelative resistivity of the deposits 21 and 22 fall to an extremely lowvalue of less than 10₃ (ohm·cm), and consequently, the electricalinfluence of the deposits 21 and 22 on the electrodes constituting theresonating parts 11 and 12 can no longer be disregarded. The deposits 21and 22 should be constituted of fine particles containing carbon and afiller constituted of Talc 3MgO.4SiO₂.H₂ O, or the like.

FIG. 5 is an electrical symbol diagram of the piezoelectric componentillustrated in FIGS. 3 and 4. A circuit structure achieved by connectingin cascade the resonating part 11 constituted of the split electrode 111and 112 and the common electrode 113 and the resonating part 12constituted of the split electrodes 121 and 122 and the common electrode123 and connecting one end of a capacitor C constituted of the capacitorelectrode 15 and the capacitor electrode 18 to the connection point ofthe two resonating parts with another end of the capacitor C connectedto the common terminal electrode 19, is assumed. The split electrode 111at the resonating part 11 is connected to the input/output terminalelectrode 13, whereas the split electrode 121 at the resonating part 12is connected to the input/output terminal 16.

FIG. 6 is a plan view illustrating another embodiment of thepiezoelectric component according to the present invention. In thefigure, the same reference numbers are assigned to components that areidentical to those in FIGS. 1 to 5. This embodiment is characterized inthat indented portions 210 and 220 constituted of through holes ornon-through holes are provided at the deposits 21 and 22. Similaradvantages to those achieved in the previous embodiment are alsorealized through this embodiment.

Next, a step for implementing the resonance frequency adjustment whichis included in the method for manufacturing a piezoelectric componentaccording to the present invention, is explained. As a specific example,center frequency adjustment performed on a ceramic filter with aselected center frequency at 10.7 MHz is explained.

FIG. 7 is a plan view of the piezoelectric component upon which thefrequency adjustment is performed. In the figure, the same referencenumbers are assigned to components that are identical to those in FIGS.1 to 6. As illustrated in FIG. 7, the deposits 21 and 22 are adheredonto the front surfaces of the resonating parts 11 and 12. The deposits21 and 22 are constituted of resin. The required indented portions 210and 220 can be formed with ease through laser beam irradiation of thedeposits 21 and 22 constituted of resin. The deposits 21 and 22 areconstituted of a resin containing a carbon filler. The desirable carbonfiller content is 0.1 to 20 wt %.

The deposits 21 and 22 are formed in a square shape with the length ofeach side at 1.1 mm over a thickness of 10 μm. However, it goes withoutsaying that they may be formed in a shape other than a square shape,such as a circular shape, another polygonal shape or the like.

FIG. 8 illustrates the method for frequency adjustment that may beimplemented with the piezoelectric component shown in FIG. 7. In thefigure, a laser beam LL having a wavelength within the range of 350 to2000 nm is radiated on the surfaces of the deposits 21 and 22 adheredonto the resonating parts 11 and 12 of the piezoelectric component 4 andthrough the irradiation of the laser beam LL, the deposits 21 and 22 aretrimmed to form the groove-like indented portions 210 and 220. Throughthis process, the divided portions 211 and 221 are obtained, and themasses of the deposits 21 and 22 are reduced so that the loads appliedto the resonating parts 11 and 12 by the deposits 21 and 22 areadjusted. By repeating this process of indented portion formation, therequired number of indented portions 210 and 220 are formed to adjustthe center frequency to a target value. The center frequency is adjustedto a value which is determined in accordance to the number of theindented portions 210 and 220, and the number, size or pattern of thedivided portions.

As explained earlier, the deposits 21 and 22 are constituted of a resinwhich, preferably, contains a carbon filler at 0.1 to 20 wt %. Table Ipresents the relationship between the carbon filler content (thequantity at which it is added), and the coefficient of variation (%),the specific resistivity (ohm·cm) and the printability.

                  TABLE I                                                         ______________________________________                                                               deposit specific                                       carbon filler                                                                          coefficient of variation                                                                    resistivity                                            content (wt %)                                                                         after trimming (%)                                                                          (Ω · cm)                                                                  printability                                ______________________________________                                        0.01     0.05˜0.15                                                                             >10.sup.14 good                                        0.05     0.05˜0.10                                                                             >10.sup.14 good                                        0.1      <0.03         >10.sup.14 good                                        0.5      <0.03         >10.sup.14 good                                        1        <0.03         >10.sup.14 good                                        5        <0.03         >10.sup.14 good                                        10       <0.03         >10.sup.14 good                                        15       <0.03         >10.sup.14 good                                        18       <0.03         >10.sup.14 good                                        20       <0.03         >10.sup.14 good                                        22       impossible to measure                                                                       <10.sup.3  good                                        25       impossible to measure                                                                       <10.sup.3  good                                        ______________________________________                                    

As indicated in Table I, when the carbon filler content is within therange of 0.1 to 20 wt %, the coefficient of variation after trimming isstabilized at a low value of less than 0.03%. Furthermore, in thisrange, the specific resistivity of the deposits 21 and 22 achieves ahigh value that exceeds 10¹⁴ (ohm·cm).

In contrast, in the range over which the carbon filler content is than0.1 wt % and in the range over which the carbon filler content is equalto or exceeds 22 wt %, the coefficient of variation after trimmingchanges over a wide range of 0.05 to 0.15 %. This is assumed to be theresult of unstable absorption of the laser beam. Moreover, when thecarbon filler content exceeds 20 wt %, the specific resistivity of thedeposits 21 and 22 falls to an extremely low value, under 10³ (ohm·cm).

Since the indented portions 210 and 220 are formed through laser beamirradiation, the number of the indented portions, their size, theirpattern and the like can be set with a high degree of accuracy. Thus,the center frequency can be set at a high accuracy value.

The indented portions 210 and 220 are formed by radiating a laser beamhaving a wavelength within a range of 350 to 2000 nm. By using a laserbeam having a wavelength within this range, the indented portions 210and 220 can be formed at the deposits 21 and 22 without resulting indegradation of the piezoelectric characteristics.

Various types of laser including excimer laser, solid-state laser, gaslaser and organic laser may be employed for laser irradiation. Anexplanation is given on a case in which a solid-state YAG laser beam isemployed, in reference to the embodiment. When employing a solid-stateYAG laser beam, one of the following, i.e., its fundamental harmonic(wavelength; 1.06 μm), its second harmonic (wavelength; 530 nm) and itsthird harmonic (wavelength; 353 nm), should be used. The wavelengths ofhigher harmonics including the fourth harmonic (wavelength; 266 nm) arein the ultraviolet light range and the processability will deteriorate.In addition, if a laser beam having a wavelength exceeding 2000 nm isirradiated, the resin will be burned by the laser beam and degradationof the piezoelectric characteristics caused by the heat will result.

When machining the indented portions 210 and 220, the center frequencyof the piezoelectric component 4 is measured with a measuring device 6prior to the machining to calculate the difference between the measuredcenter frequency and a target center frequency. Then, the number ofrequired indented portions 210 and 220 is determined through aconversion formula for the number of indented portions 210 and 220 andthe quantity of the center frequency shift.

FIG. 9 illustrates the relationship between the number of indentedportions and the center frequency shift quantity (kHz). These data areused when forming indented portions 210 and 220 as grooves with a widthof 33 μm and a length of 1 mm, by employing the fundamental harmonic ofthe solid-state YAG laser. As illustrated in the figure, the centerfrequency shifts by approximately 4 kHz per groove-like indentedportion. This shift is made in the direction in which the centerfrequency increases, i.e., toward the higher frequency. Thus, theconversion formula for the number of indented portions 210 and 220 andthe center frequency shift quantity to be adopted in this embodiment isexpressed as:

number of indented portions=(target center frequency-measured centerfrequency) kHz/4 kHz

It is to be noted that, since it is necessary to achieve identicalfrequency characteristics at the two resonating parts 11 and 12 in theceramic filter in this embodiment, the same machining must be performedto form identical indented portion at the two resonating parts 11 and12.

In the embodiment illustrated in FIG. 8, a measuring device 6 formeasuring the center frequency of the piezoelectric component 4 isprovided, the data in regard to the center frequency obtained at themeasuring device 6 are sent to a laser apparatus 5 and the requirednumber of indented portions is calculated at the laser apparatus 5 incorrespondence to the degree of deviation of the measured centerfrequency relative to the target center frequency. Then, the intervalsover which the indented portions are to be machined are calculated basedupon the dimensions of the deposits 21 and 22, the number of indentedportions, the width of the indented portions and the like, and incorrespondence to the results of the calculation, the laser beam LL isradiated onto the deposits 21 and 22 to form the indented portions 210and 220.

Now, the test example described above and its results are explained. Inthe test, indented portions were machined at the deposits of theindividual elements in an aggregated substrate constituted of aplurality of substrates by using the fundamental harmonic of asolid-state YAG laser. FIG. 10 presents a graph indicating the frequencydistribution of the center frequencies. As the figure indicates, whilethe center frequencies of the piezoelectric components wereinconsistent, ranging from 10.58 to 10.66 MHz in the pre-adjustmentmeasurement, almost the entire number n of the piezoelectric componentson the aggregated substrate were adjusted to achieve a center frequencyof 10.7 MHz through the adjustment.

Next, a means that is suited for adjustment of the resonancecharacteristics of an oscillator, and a resonator is explained. FIGS. 11to 13 illustrate an example of a ceramic oscillator. However, thepiezoelectric component may be constituted as a filter or the likeinstead of an oscillator.

As illustrated in the figures, the piezoelectric component according tothe present invention includes a piezoelectric substrate 1 and at leastone deposit 2. The piezoelectric substrate is formed in a plate shapeusing a piezoelectric ceramic material in the known art. Thepiezoelectric substrate is provided with at least one resonating part 3.The resonating part 3 includes a front electrode 31 and a rear electrode32. The front electrode 31 is provided at the front surface of thepiezoelectric substrate 1, whereas the rear electrode 32 is provided atthe rear surface of the piezoelectric substrate 1. The front electrode31 and the rear electrode 32 face opposite each other across thepiezoelectric substrate 1. At the front surface of the piezoelectricsubstrate 1, a front lead electrode 33 and a first terminal electrode 34are provided. The front electrode 31 is connected to the front leadelectrode 33 which, in turn, is connected to the first terminalelectrode 34. A rear lead electrode 35 is provided at the rear surfaceof the piezoelectric substrate 1. A second terminal electrode 36 isprovided at the front surface of the piezoelectric substrate 1. The rearelectrode 32 is connected to the rear lead electrode 35, and the rearlead electrode 35 and the second terminal electrode 36 are connectedwith each other via a through hole conductor 37.

The deposit 2 is added onto the resonating part 3. In the embodiment,the deposit 2 is adhered to cover the front electrode 31 constitutingthe resonating part 3. Although not shown, the deposit 2 may be providedat the rear electrode 32 as well as at the front electrode 31 or thedeposit 2 may be provided at the rear electrode 32 only. The deposit 2is constituted of resin. An ultraviolet light setting resin isparticularly suited for this purpose. The resin is adhered by means suchas coating to cover the entire surface of the front electrodeconstituting the resonating part 3.

The surface of the deposit 2 is constituted of indentations andprojections, and when the surface roughness of the indented andprojected surface is assigned Rmax and the resonance wavelength at theresonating part 3 is assigned λ₀, the standardized surface roughness R₀defined as (Rmax/λ₀) satisfies 0<R₀ ≦0.008.

FIG. 14 is a sectional view that schematically illustrates theindentations and projections at the surface of the deposit 2. Thesurface of the deposit 2 is a rough surface having a great number ofminute projections 21. The a real density of the projections 21 may be,for instance, approximately 10,000/1 mm². The surface roughness Rmaxdetermined based upon the depth of the valley portions between theprojections and the height of the apex of the projections 21 isapproximately 1.0 μm in an example in which the standardized surfaceroughness R₀ =0.008 and the resonance frequency at the resonating part 3is 40 MHz. At the indented and projected surface of the deposit 2, it isdesirable that the valley portions 22 formed between the projections 21do not reach the front surface of the piezoelectric substrate 1.

As explained above, since the deposit 2 is added onto the resonatingpart 3 in the piezoelectric component according to the presentinvention, the resonance characteristics at the resonating part 3 areadjusted in correspondence to the mass of the deposit 2.

Since the surface of the deposit 2 is constituted as a surface havingindentations and projections, the mass of the deposit 2 is finelycontrolled in correspondence to the state of the indentations andprojections at the surface of the deposit 2. Thus, a piezoelectriccomponent having a resonance frequency that is finely controlled with ahigh degree of accuracy is achieved.

The Q value of the resonance characteristics is greatly affected by thestate of the indentations and projections at the surface of the deposit2. FIG. 15 illustrates the relationship between the standardized surfaceroughness R₀ and the Q value. As the figure indicates, in the range overwhich the standardized surface roughness R₀ is equal to or less than0.008, a high Q value which is almost constant is achieved, regardlessof variations in the surface roughness R₀.

In the range over which the standardized surface roughness R₀ is equalto or greater than 0.008, the Q value becomes lower almost linearly asthe standardized surface roughness R₀ increases.

Next, a step for implementing the resonance frequency adjustment that isincluded in the method for manufacturing a piezoelectric componentaccording to the present invention is explained. The explanation isgiven on an example in which a ceramic oscillator having an oscillationfrequency of 40 MHz, which utilities a thicknesswise longitudinalvibration mode is obtained as a specific example of the piezoelectriccomponent, in reference to this embodiment.

FIG. 16 is a plan view illustrating another embodiment of thepiezoelectric component with which the resonance frequency adjustment isperformed. In the figure, the same reference numbers are assigned tocomponents identical to those in FIG. 11. As illustrated in FIG. 16, thedeposit 2 is applied onto a front surface of a front electrode 31 whichis formed in a circular shape with a diameter of 0.8 mm. An ultravioletlight setting resin is used to constitute the deposit 2 and theultraviolet light setting resin is coated in a quadrangular shape andthen is caused to set through irradiation with ultraviolet light. Thedeposit 2 was coated in a square shape with the length of each side at1.1 mm over a thickness of 5 μm. However, it goes without saying thatthe deposit 2 may be applied in a circular shape or any other polygonalshape instead of such a square shape.

FIG. 17 illustrates a method for resonance frequency adjustmentimplemented on the piezoelectric component illustrated in FIG. 16. Asshown in the figure, a laser beam LL is radiated onto the surface of thedeposit 2 added onto the resonating part 3 of the piezoelectriccomponent 4 and then the laser beam L1, is scanned to trim the surfaceof the deposit 2. The wavelength of the laser beam LL employed for thispurpose should be equal to or less than 350 nm. The laser beam LL isgenerated by the laser apparatus 5. Various types of laser, including anexcimer laser, a solid-state laser, a gas laser, an organic laser andthe like may be used as the laser apparatus 5. In the embodiment, asolid-state YAG laser was used. When a solid-state YAG laser is used,the requirement that the wavelength of the laser beam LL must be equalto or less than 350 nm is satisfied by using the laser beam at thefourth harmonic, which has a wavelength of 266 nm.

Since, by using a laser beam having a wavelength of 350 nm or less totrim the surface of the deposit 2, the surface of the deposit 2 can betrimmed evenly to achieve a standardized surface roughness R₀ of 0.005or less, a high degree of accuracy for the resonance frequency and ahigh Q value can be set. It has been confirmed that the Q value becomeslower if the trimming is performed using a laser beam having awavelength greater than 350 nm, e.g., a laser beam having a wavelengthof 353 nm.

During the trimming process, by measuring the resonance frequency of thepiezoelectric component and radiating the laser beam LL, which iscontrolled in correspondence to the degree of deviation in the measuredresonance frequency relative to a target resonance frequency, at thedeposit 2, the resonance frequency can be easily adjusted to the targetresonance frequency. In the embodiment illustrated in FIG. 17, themeasuring device 6 which measures resonance frequencies of piezoelectriccomponents is provided so that the data of the resonance frequencyobtained at the measuring device 6 are sent to the laser apparatus 5which, in turn, irradiates the laser beam LL controlled incorrespondence to the degree of deviation in the measured resonancefrequency relative to the target resonance frequency at the deposit 2.By repeating this adjustment, the adjustment accuracy of the resonancefrequency can be raised to a higher level.

Since the wavelength of the laser beam LL, which is radiated onto thedeposit 2 is equal to or less than 350 nm, only an extremely smallquantity of the laser light LL is converted to heat. Consequently, theresonance frequency of the piezoelectric component can be measured evenimmediately after irradiation by the laser beam LL. Thus, it is possibleto repeat the trimming adjustment employing the laser beam LL withouthaving to allow time intervals.

FIG. 18 presents data that indicate the relationship between the lengthof elapsed (sec) and the resonance frequency shift quantity (%). Thecurve L1 represents the characteristics achieved when the fundamentalharmonic (wavelength; 1.06 μm) of a solid-state YAG laser is used andthe curve L2 represents the characteristics achieved when the fourthharmonic (wavelength; 266 nm) of the solid-state YAG laser is used. Asthe characteristics curve L2 demonstrates, when the fourth harmonic(wavelength; 266 nm) having a wavelength equal to or less than 350 nm isused, the oscillation frequency shift quantity immediately afterirradiation with the laser beam is small and, furthermore, thefluctuation in the oscillation frequency converges to a constant valuewithin a short length of time. As a result, a series of tasks such asre-measurement and fine adjustment can be implemented promptly withouthaving to allow time intervals. In contrast, if the fundamental harmonic(wavelength; 1.06 μm) is used, the resonance frequency shift quantityimmediately after the laser beam irradiation is large and, furthermore,since the resonance frequency fluctuation lasts a long time, asindicated by the characteristics curve L1, the series of tasks includingre-measurement and fine adjustment cannot be implemented promptly.

Either a single-mode or multi-mode laser beam LL may be employed. Ofthese, a multi-mode laser beam is especially suitable. FIG. 19illustrates the laser intensity characteristics in the direction of theradius of the spot of a single-mode laser beam, whereas FIG. 20illustrates the laser intensity characteristics in the direction of theradius of the spot with a multi-mode laser beam. As is obvious from acomparison of FIGS. 19 and 20, the intensity distribution within thespot of the multi-mode laser beam is flatter than that of thesingle-mode laser beam. As a result, the surface can be trimmed moreeasily through irradiation of a multi-mode laser beam.

As has been explained, the fourth harmonic of a solid-state YAG laser isparticularly suited when a multi-mode laser beam is employed. FIG. 21schematically illustrates a state that is achieved when the deposit 2 istrimmed by using a single-mode laser beam constituted at the fundamentalharmonic (wavelength; 1.06 μm) of a solid-state YAG laser. Asillustrated in the figure, the surface roughness Rmax achieved throughthe trimming is relatively large, reaching 4 to 5 μm in the case of thedeposit 2 having a thickness of 5 μm. Since a ceramic oscillatorachieving a resonance frequency λ₀ of 40 MHz is to be obtained in theembodiment, Rmax calculated through the conversion formula for thestandardized surface roughness described earlier must be 1.0 μm or less,and thus, Rmax reaching 4 to 5 μm greatly deviates from thisrequirement.

FIG. 22 schematically illustrates a state achieved by trimming thedeposit 2 using a single-mode laser beam constituted at the fourthharmonic (wavelength; 266 nm) of a solid-state YAG laser. As illustratedin the figure, the surface roughness Rmax achieved through the trimmingis smaller than that achieved by employing a single-mode laser beamconstituted at the fundamental harmonic. Even so, the surface roughnessRmax is in a range of 1 to 3 μm, and there is a difficulty in satisfyingthe requirement that the surface roughness Rmax must be smaller than 1.0μm.

FIG. 23 schematically illustrates a state achieved by trimming thedeposit 2 using a multi-mode laser beam at the fourth harmonic(wavelength; 266 nm) of a solid-state YAG laser. As illustrated in thefigure, the surface roughness Rmax can be set at 0.1 μm or smaller.

Furthermore, as explained earlier, since a multi-mode laser beamachieves a flatter intensity distribution within the spot compared to asingle-mode laser beam LL, the surface can be trimmed more consistentlyby irradiating with a multi-mode laser beam LL to ensure that hardly anydegradation of the Q value occurs.

Alternatively, trimming may be performed by evenly scanning the spot ofthe laser beam LL over the entire surface of the deposit. The quantityby which the resonance frequency shifts per scan described above isconstant. As a result, the resonance frequency can be adjusted incorrespondence to the number of times that a scan is performed with thespot of the laser beam LL.

Next, a test example of the scanning described above and its results areexplained. In the test, a solid-state YAG laser was employed to scan aspot of a multi-mode laser beam LL at the fourth harmonic. The test wasconducted under the following conditions: the laser intensity at thesurface of the deposit at 10 mW; the spot diameter at 10 μm; the Qswitch frequency at 10 kHz; the scan speed at 1000 mm/sec; and the scanarea at 1.0 mm×1.0 mm.

FIG. 24 illustrates the relationship between the number of full-surfacescans and the quantity of resin trimmed in the direction of the depth ofthe resin constituting the deposit. As the figure indicates,approximately 0.25 μm of the resin is trimmed per full-surface scan.Through this, the resonance frequency is adjusted.

FIG. 25 illustrates the relationship between the number of full-surfacescans and the quantity of resonance frequency shift (kHz). As indicatedin the figure, the resonance frequency shifts by approximately 20 kHztoward the higher frequency side per full-surface scan. Based upon theseresults, the number of scans to be performed can be determined throughthe following formula.

    number of scans={(target resonance frequency)-(measured resonance frequency)}/20 kHz

In addition, a pulse oscillation type laser system may be employed toradiate a pulse laser beam evenly over the entire surface of the depositinstead.

The quantity by which the resonance frequency shifts as a result of oneirradiation described above is constant. Consequently, the resonancefrequency can be adjusted in correspondence to the number of times thepulse laser beam is radiated in a manner similar to that describedearlier.

A test for ascertaining the relationship between the standardizedsurface roughness R₀ and the Q value and its results are now explained.For the testing, a multi-mode laser beam at the fundamental harmonic, asingle-mode laser beam at the fourth harmonic and a multi-mode laserbeam at the fourth harmonic, of a solid-state YAG laser were used.

One scan was conducted using the multi-mode laser beam at thefundamental harmonic under the following scanning conditions:

spot diameter at 50 μm;

Q switch frequency at 15 kHz;

scan speed at 300 mm/sec;

laser output at 0.5 W, 0.6 W and 0.7 W.

Ten scans were conducted using the single-mode laser beam at the fourthharmonic under the following scanning conditions:

spot diameter at 10 μm;

oscillation Q switch frequency at 10 kHz;

scan speed at 1000 mm/sec;

laser output at 10 mW, 15 mW, 20 mW and 25 mW.

Ten scans were conducted using the multi-mode laser beam at the fourthharmonic under the following scanning conditions:

spot diameter at 10 μm;

oscillation frequency at 10 kHz;

scan speed at 1000 mm/sec;

laser output at 10 mW and 25 mW.

FIG. 26 presents data indicating the relationship between thestandardized surface roughness R₀ and the Q value which were obtainedthrough the test described above. It is difficult to satisfy therequirement that the standardized surface roughness R₀ be at or lessthan 0.008 with the multi-mode laser beam at the fundamental harmonic.The requirement that the standard surface roughness R₀ be at or lessthan 0.008 is still not fully satisfied by using the single-mode laserbeam at the fourth harmonic. However, with the multi-mode laser beam atthe fourth harmonic, the requirement that the standardized surfaceroughness R₀ be at or less that 0.008 is fully satisfied.

Furthermore, according to the present invention, the individualresonance frequencies of a great number of piezoelectric components thattend to deviate greatly can be adjusted to a constant target resonancefrequency with a high degree of accuracy.

Next, an example of testing to substantiate the forgoing and its resultsare explained. In the test, a great number of the piezoelectriccomponents, one of which is illustrated in FIG. 16, were prepared andtheir resonance frequencies were adjusted to 40.0 MHz by irradiatingwith a multi-mode laser beam LL at the fourth harmonic using asolid-state YAG laser. The test was conducted under the followingconditions

spot diameter at 10 μm;

oscillation frequency at 10 kHz;

scan speed at 100 mm/sec.

The number of scans to be performed was determined by using thefollowing formula.

    number of scans={(40,000 kHz)-(measured resonance frequency)}/25 kHz

Note that the number of scans to be performed was calculated as aninteger value with the numerals after the decimal point rounded off.FIG. 17 is a graph illustrating the frequency distribution of theresonance frequencies. As the figure indicates, the resonancefrequencies of the piezoelectric oscillator parts were inconsistent,ranging from 39.6 MHz to 39.9 MHz in the pre-adjustment measurement. Themeasurement performed after the adjustment demonstrates that theresonance frequencies of almost all the piezoelectric components wereconsistent at 40.0 MHz.

While the resonance frequencies of piezoelectric components using athicknesswise longitudinal vibration mode are adjusted, resonancefrequencies of piezoelectric components employing a thicknesswise slipvibration mode can be adjusted in a similar manner.

What is claimed is:
 1. A piezoelectric component comprising:apiezoelectric substrate provided with at least one resonating part; andat least one resin deposit having enclosing outer edges and beingadhered onto a covered surface portion of said at least one resonatingpart, said resin deposit having a filler that improves a lightabsorption characteristic of the deposit and a plurality of indentedportions in an exterior surface away from the surface portion.
 2. Thepiezoelectric component of claim 1, wherein said indented portions areor holes grooves or holes.
 3. The piezoelectric component of claim 1,wherein said indented portions pass through said deposit.
 4. Thepiezoelectric component of claim 1, wherein said indented portions havea depth smaller than the thickness of said deposit.
 5. The piezoelectriccomponent of claim 1, wherein said indented portions form a stripepattern or a lattice pattern.
 6. The piezoelectric component of claim 1,wherein said indented portions are formed as holes or as anisland-shaped pattern.
 7. The piezoelectric component of claim 1,wherein said filler is a carbon filler in the range of 0.1 to 20 wt %and said resin is electrically insulating.
 8. The piezoelectriccomponent of claim 1, wherein the exterior surface has projectionsbetween said indented portions, said indented portions and projectionsdefining a surface roughness Rmax of said exterior surface satisfyingthe condition that;0<Rmax/λ₀ ≦0.008 with λ₀ representing a resonancewavelength of said resonating part.
 9. The piezoelectric component ofclaim 8, wherein said surface roughness Rmax is equal to or less than1.0 μm.
 10. The piezoelectric component of claim 1, wherein said resinis electrically insulating.
 11. The piezoelectric component of claim 1wherein said resin is also of an ultraviolet light setting resin.